The present invention pertains to an automated exposure control unit and method for image recording devices and is, particularly, adapted for use in conjunction with cameras employing strobes for exposing photographic film of the self-developing type.
Capturing a properly exposed scene on film is often difficult and a wide variety of techniques have been put forth in the prior art to achieve that end in an economical manner. Proper exposure is especially difficult when a photographer is confronted with a wide variety of scene lighting and subject conditions. Correct exposure is even more difficult when the exposure employs an electronic strobe for illuminating the subject and scene. The foregoing difficulties are compounded when exposing self-developing film in low cost mass-market cameras; wherein conventional techniques of improving film picture quality done during film processing cannot be utilized and sophisticated electronic systems do not make economic sense.
Despite the problems associated with obtaining correct exposures, there are several known successful techniques for dealing with the above issues by providing enhanced exposure for a variety of scene lighting and subject conditions. For instance, commonly-assigned, U.S. Pat. No. 4,192,587 describes a proportional fill flash system for varying the time at which a source of artificial illumination is energized relative to an exposure interval by determining the range of a subject and to thereafter utilize the ranging information to vary the time in which the flash is fired so that it fires at an aperture corresponding to subject range. Commonly assigned U.S. Pat. No. 4,255,030 describes a proportional fill flash system utilizing quenching of a quench strobe at an appropriate time without determining subject range based on the integration of both ambient and flash. Commonly assigned U.S. Pat. No. 4,285,584 describes a proportional fill flash system utilizing a photometer having three zones in its overall field of view for distinguishing between background, central, and foreground portions of the scene. The output of the different segments of the scene are compared to increase or decrease the exposure depending on whether the scene is more heavily illuminated in the background or foreground. Commonly assigned U.S. Pat. No. 4,423,936 describes an exposure control unit utilizing a photometer having a multi-sensor array that detects both subject range and ambient light intensity. A comparison of range measurements identifies that scene area having the nearest object to the ambient light intensity measurements of subject and non-subject areas in order to classify scene lighting conditions and then select a corresponding program which controls the operation of the system to vary the ratio of ambient to artificial light contributions to exposure.
Despite the success of the above approaches in addressing the foregoing concerns particularly in regard to self-developing instant cameras, there is nevertheless a continuing desire to improve upon the efficiency and costs of obtaining proper exposure not only with cameras of the foregoing kind but also with digital cameras as well. In regard to digital cameras, it is highly desirable to effect highly quality printing utilizing low cost methodologies. For instance, in a camera with a digital capture mode the use of a multi-sensor array to minimize the problem adds to the overall cost to a system. Moreover, it is highly desirable to achieve the foregoing in a variety of scene lighting conditions wherein artificial illumination makes a contribution.
An object of the invention is to control the photographic exposure automatically such that the subject and non-subject areas of a scene are correctly exposed in an economical and efficient manner.
It is another object of the invention to provide a digital capture system which can utilize the material already in the system.
To achieve this and other objects, the invention is directed to a method of controlling exposure to a photosensitive element by controlling illumination of the scene through a comparison of brightness and range mapping. The method comprises: (a) sensing image data from the scene including scene brightness from a first set of a plurality of regions in the scene; (b) forming a brightness map of the scene in accordance with the brightness data corresponding to the first set of regions; (c) sensing range data from a second set of regions in the scene; (d) forming a range map to determine a subject in the scene; and, (e) comparing the range map with the scene brightness map for determining a relationship between scene brightness and the subject brightness; and, (f) controlling the exposure by controlling artificial illumination upon the scene, whereby a relationship of ambient and artificial illumination is generally maintained.
The invention is further directed to a system for controlling exposure by controlling the relationship between ambient and artificial illumination during exposure. The system comprises a sensor for sensing image data including scene brightness from a first set of a plurality of regions in a scene; a sensor for sensing range data from a second set of regions in the scene; and, processing means for (i) defining a brightness map of the scene in accordance with the brightness data corresponding to the first set of regions, (ii) defining a range map of the scene in accordance to the second set of regions to determine a subject in the scene, (iii) comparing the range map with the scene brightness map for determining a relationship between scene brightness and the subject range; and, (iv) controlling the exposure during an exposure interval by controlling artificial illumination upon the scene, whereby a relationship of ambient and artificial illumination is generally maintained.
As a result of the foregoing system and method, when the ambient brightness readings of both the scene background and scene subject are measured, control of the ambient exposure of the background is controlled by the ambient background readings and the exposure of the subject is controlled by a comparing the subject brightness to the scene brightness and by controlling the amount of artificial illumination directed at the subject by the source of artificial illumination to make up the difference in brightness values in order to give correct exposure for both the scene background and the subject. Accordingly, both the scene subject and scene background are wellexposed.